870. Reducing prolonged sedentary time using a treadmill desk acutely improves cardiometabolic risk markers in male and female adults
Commentary by Dr Paddy Dempsey, Baker Heart and Diabetes Institute, Australia
In developed countries, and in the rapidly urbanizing populations of developing countries, too much sitting as distinct from too little exercise has become the default behavioural option – inextricably embedded in work, school, transport, and leisure. High volumes of sitting, and potentially prolonged uninterrupted periods of sitting (typically defined as >30-60 min continuous sitting), are risk factors for non-communicable diseases such as type 2 diabetes, heart disease, and premature mortality. Office-based workers in particular spend >70% of their working hours seated, and accumulating acute experimental evidence suggest that “breaking up” prolonged sitting with brief, frequent bouts of light-intensity walking is beneficial for cardiometabolic health. Reducing prolonged periods of sitting has therefore emerged as a new focus for reducing the risk of cardiometabolic diseases.
This acute laboratory study conducted by Champion et al. was in 24 sedentary, but otherwise healthy, men and women. In a randomized, cross-over study design, it examined whether interrupting 6.5 hours of prolonged sitting with a total of 2 hours of light-intensity walking using a treadmill desk (accumulated in 20 minute bouts across the day – i.e. the final 20 minutes of each hour) improved post-meal cardiometabolic risk markers. Relative to uninterrupted sitting, accumulating 2 hours of light-intensity walking lead to acute reductions in post-meal glucose (↓38%) but not insulin (indicating muscle contraction-stimulated glucose uptake was the primary mechanism of benefit), reduced triglycerides (↓32%) and reduced systolic/diastolic blood pressure (↓3/4%, or 3-4 mmHg) over the 6.5 hours.
These findings are yet another reminder that accumulating more physical activity across the day, even at very light-intensities, is important for reducing the increased cardiometabolic risk associated with prolonged sitting. The 2 hour sitting-reduction target employed in the present study was based a priori on recommendations that “desk-based employees should initially accumulate a minimum of 2 h/day of light-intensity activity during working hours to benefit their health” (Buckley et al., 2015). However, limited evidence exists to support such quantitative targets at present, which are based largely on observational/retrospective studies and short-term intervention studies. Indeed, current national physical activity guidelines are not yet able to provide specific recommendations about the quantity or duration of sitting time that is harmful to health, nor how often and with what (e.g. standing/walking) sitting time is best replaced. More long-term intervention studies are clearly needed, in a variety of sub-populations, and future refinements to potential quantitative recommendations will be required as more evidence is published.
An important consideration in relation to the present study and real-world practice/policy efforts is the feasibility of 2 hour sitting-reduction targets, as well as the feasibility, cost-effectiveness and acceptability of treadmill workstations in the workplace. For example, effect sizes from a meta-analytic review (Martin et al., 2015) focussing on sedentary behaviour interventions (albeit mostly low quality) and a multicomponent intervention trial aiming to reduce adult sitting time with activity permissive workstations (Healy et al., 2016) range from 42 min/day to 45 min/8-hour day, with almost all of the reductions in sitting time in the latter intervention trial replaced by standing rather than walking. Treadmill workstations could viably assist in promoting positive changes in physical activity behaviours among office workers; however, health benefits will need to be weighed alongside potential space/cost considerations and any effects on workplace productivity, shared vs. personal access issues, and any potential compensatory effects on leisure-time activity behaviours or adverse musculoskeletal effects.
On the other hand, many previous experimental studies that have prescribed very-brief bouts of standing and light walking (usually 2-5 min bouts every 30-60 min, generally reducing overall sitting by around 30-60 minutes across a 6-7 hour period) have also shown cardiometabolic benefits, albeit generally of lower magnitude (Dempsey et al., 2016). Thus, the important message here is a ‘whole of day’ approach to reducing sitting time and accumulating more movement (preferably ambulation) across the entire day, as well as the avoidance of sustained periods spent in one posture. Indeed, the prolonged periods of sitting that now characterise much of our day-to-day lives – especially our working lives – should be seen as ‘missed opportunities’ for healthy movement. Future research on the attributes of urban environments and workplaces that promote too much sitting is also warranted, along with innovative, low cost, and sustainable behaviour-change and environmental strategies that can reach a large proportion of the population who are at increased risk of cardiometabolic diseases.
Source: Journal of Sports Sciences
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